| 摘要 |
PURPOSE:To decrease the effect of adjacent light sources on each other by a method wherein light sources are driven by a periodically modulated current whose frequency is higher than a specified value, where a threshold current which starts generating an oscillation is between the maximum and the minimum amplitude of the modulated current. CONSTITUTION:In a usual semiconductor laser, the optical output is nearly proportional to the variation of a drive current when the drive current is equal to or larger than a threshold current Ith. Therefore, provided that a drive direct current required for obtaining an average optical output P denotes (Ip+Ith), the average optical output of a laser driven by a square pulse of 50% duty whose minimum and maximum value are Ith and (2XIp+Ith) respectively is also equal to P. If the drive current is less than the threshold current Ith, the laser does not start oscillating, so that the optical output is the same even if the minimum value of a drive pulse is less than Ith. On the other hand, if the minimum value is made smaller than Ith, the average drive current becomes smaller than (Ip+Ith). Therefore, the rise of temperature becomes small. If the period of a pulse is smaller than a time constant of the heat interference, the rise of temperature can be considered to be nearly the same as a direct current drive, so that it is sufficiently effective if the period of a pulse is 1kHz or more. |
